Temperbead Repair CA-6NM
Temperbead Repair CA-6NM
(OP)
I am prepared a PQR test report for qualification of a temper-bead butt repair on CA-6NM martensitic material to ASME IX. As part of the testing we are performing tensile, bend tests, macro and hardness. The WPS specifies a temper-bead repair using a minimum preheat 120 C. The weld metal is E410NiMo-26. The thickness of the plate is 18mm. For a hardness, the maximum HAZ hardness is 373 HV. The weld metal hardness ranges from 325 to 348 HV. I was expecting to achieve maximum of 350 HV. Weld is good quality with no defects. Are these hardness results acceptable to ASME IX?





RE: Temperbead Repair CA-6NM
A characteristic of 410NiMo welds is that the deposit is generally harder than the hardest part of the HAZ, the more usual target of temper bead welding. (I will assume that 309 filler is not an option, although it is frequently used when PWHT is not possible.)
When it comes to preheat of CA-6NM, sometimes more is less. For 18mm plate, minimum preheat could actually be a little lower, say 100°C. The key thing is to strictly control the interpass to not more than 260°C. Due to extreme suppression of the Ms temperature, mainly by nickel, overheating during welding can result in extreme hardness after cooling due to austenite transforming in bulk to untempered martensite - disastrous for toughness and risk of hydrogen cracking. ALL welding of CA-6NM benefits from a temper bead approach, which is why electrode diameter and bead size should be limited (5/32"Ø for SMAW, 1/16"Ø for FCAW). Stringer beads only.
Have you examined the deposit chemistry of the electrode (as per AWS A5.4)? Back in the day, building hydro turbines with seld sections up to 6" thick, I ordered hardness testing with every heat/lot of FCAW wire.
Remember to qualify each welder to the same procedure and hardness limit. Consider welding with excess reinforcement, such that the untempered final passes are completely removed.
"If you don't have time to do the job right the first time, when are you going to find time to repair it?"
RE: Temperbead Repair CA-6NM
RE: Temperbead Repair CA-6NM
RE: Temperbead Repair CA-6NM
"If you don't have time to do the job right the first time, when are you going to find time to repair it?"
RE: Temperbead Repair CA-6NM
RE: Temperbead Repair CA-6NM
RE: Temperbead Repair CA-6NM
RE: Temperbead Repair CA-6NM
For hydro turbine equipment you are not forced (unless by client specification) to meet the ASME bend test criterion. Even if you do everything possible to get the hardness lower, I think passing the Section IX criterion is borderline at best. I suggest a 90° acceptance criterion would suffice. 309 might not make bend test problems disappear completely, due to the abrupt hardness step at the fusion line.
Did you qualify on 3/8" thickness? Because probably face bends will be more difficult than side bends.
Just by the way, anyone know of CA-6NM turbines being repaired with duplex stainless? Strength would be good, but I've no idea of cavitation performance.
"If you don't have time to do the job right the first time, when are you going to find time to repair it?"
RE: Temperbead Repair CA-6NM